Pham Huu Sach

Characterizations of generalized convexities via generalized directional derivatives

The paper gives characterizations of convexity, quasiconvexity, invexity and pseudoconvexity for a (radially) upper-semicontinuous function f in a topological vector space via appropriate properties of a bifunction which is majorized by the upper radial derivative of f and which stands for a generalized derivative of some sort.

New Scalarizing Approach to the Stability Analysis in Parametric Generalized Ky Fan Inequality Problems

This paper gives sufficient conditions for the upper and lower semicontinuities of the solution mapping of a parametric mixed generalized Ky Fan inequality problem. We use a new scalarizing approach quite different from traditional linear scalarization approaches which, in the framework of the stability analysis of solution mappings of equilibrium problems, were useful only for weak vector equilibrium problems and only under some convexity and strict monotonicity assumptions. The main tools of our approach are provided by two generalized versions of the nonlinear scalarization function of Gerstewitz. Our stability results are new and are obtained by a unified technique. An example is given to show that our results can be applied, while some corresponding earlier results cannot.

Generalized Vector Quasivariational Inclusion Problems with Moving Cones

AbstractThis paper deals with the generalized vector quasivariational inclusion Problem (P1) (resp. Problem (P2)) of finding a point (z0,x0) of a set E×K such that (z0,x0)∈B(z0,x0)×A(z0,x0) and, for all η∈A(z0,x0),

Strong Duality with Proper Efficiency in Multiobjective Optimization Involving Nonconvex Set-Valued Maps

\begin{array}{l}F(z_0,x_0,\eta)\subset G(z_0,x_0,x_0)+C(z_0,x_0)\cr \mathrm{[resp.}F(z_0,x_0,x_0)\subset G(z_0,x_0,\eta)+C(z_0,x_0)],\end{array}

Existence Results in a General Equilibrium Problem

where A:E×K→2K, B:E×K→2E, C:E×K→2Y, F,G:E×K×K→2Y are some set-valued maps and Y is a topological vector space. The nonemptiness and compactness of the solution sets of Problems (P1) and (P2) are established under the verifiable assumption that the graph of the moving cone C is closed and that the set-valued maps F and G are C-semicontinuous in a new sense (weaker than the usual sense of semicontinuity).

Another characterization of convexity for set-valued maps

This paper gives sufficient conditions for the continuity of the solution mappings of parametric non-weak vector Ky Fan inequality problems with moving cones. The main results of the paper are new and are obtained under an assumption different from the known density hypothesis. They are written in terms of nonlinear scalarization functions associated to the data of the problems under consideration. Verifiable conditions are given, and examples are provided.

Solution Existence in Bifunction-Set Optimization

In this paper, we consider some dual problems of a primal multiobjective problem involving nonconvex set-valued maps. For each dual problem, we give conditions under which strong duality between the primal and dual problems holds in the sense that, starting from a Benson properly efficient solution of the primal problem, we can construct a Benson properly efficient solution of the dual problem such that the corresponding objective values of both problems are equal. The notion of generalized convexity of set-valued maps we use in this paper is that of near-subconvexlikeness.

Lower Semicontinuity Results in Parametric Multivalued Weak Vector Equilibrium Problems and Applications

New sufficient conditions are given for the existence of solutions of a Henig proper generalized vector quasiequilibrium problem with moving cones. They are established by a new scalarizing approach, which is based on a suitable nonlinear scalarization function, proposed recently for set-valued maps in Sach and Tuan (J. Optim. Theory Appl. 157:347–364 (2013)). Examples are given to illustrate our main results.